1. Field of the Invention
The present invention relates, generally, to a gripper apparatus and, more specifically, to an electroadhesive gripper apparatus.
2. Description of the Related Art
Gripper apparatuses can use the principle of electroadhesion in order to exert a retention force on an object that is to be gripped or retained. For this a static electric potential in particular is applied to at least one electrode of an electroadhesive gripper apparatus. As a result, a static electric field, in particular, is generated. If the electrodes of an electroadhesive gripper apparatus are positioned in the proximity of the surface of an object that is to be gripped, an electroadhesive force can be exerted by the gripper apparatus on the object to be gripped via the electric field.
There is the problem thereby that the functional range of the electroadhesion force around the electrode is very small. Thus, in order to be able to reliably grip and retain an object, the spacing between the surface of the object that is to be gripped and the electrodes should be very small. For this reason, mainly electroadhesive gripper apparatuses for manipulating flat components, such as semiconductor wafers for example, are described in the prior art.
In particular, a gripping and retaining of uneven objects is problematic. Due to the limited range of the electroadhesion force, picking up objects is also problematic if the electroadhesive gripper apparatus cannot be placed directly on the object that is to be gripped. An electroadhesive gripper apparatus exhibits in this regard only a limited penetration. A step height can only be attained with difficulty. For this reason, it is difficult to make a targeted selection from numerous objects arranged adjacent to one another, or to only pick up specific objects. Furthermore, the described gripper apparatuses are only suited to a limited extent for separating objects in a collection of numerous objects. Lastly, the releasing of an object from the electroadhesive gripper apparatus can also be problematic, because, for example, with non-conductive objects, and electrostatic charge may occur.
An electroadhesive gripper apparatus is described in US 2011/0110010 A1, which has a flat extending, but flexibly bendable, gripper surface, in which electric sections are incorporated for exerting an electroadhesion force.
A multi-function carrier, in particular for a gripper, is described in DE 103 19 272 A1. The multi-function carrier has a flat carrier substrate, serving as a bearing surface. Electric sections for exerting an electroadhesion force on an adjoining object are provided in the plane of the carrier substrate. Furthermore, flow-through openings for a Bernoulli suction device and for other vacuum retaining apparatuses are provided in the bearing plane. The multi-function carrier serves to affix flat workpieces, such as semiconductor wafers, for the manipulation thereof, wherein, to a certain extent, curvatures in the flat workpieces can be compensated for. For this, the workpiece that is to be affixed with a comparably strong suction force by the Bernoulli suction device are suctioned onto the bearing surface and brought into the effective range of the electrodes for exerting an electroadhesion force. Larger surface irregularities cannot, however, be compensated for.